REplacing water heater - PV, DV, or Tankless?

Hey folks!

Here in Ontario it's common to rent a water heater. Yes, it's absurd, and yes, I want to stop handing out $26/month to the rental company.

We currently have an 8 year old Rheem Power Vent 50 gallon tank. Its size is good enough for our family needs (2 adults, 2 kids that will be teens within a decade). However, the space it is taking up could greatly benefit us, which is one key reason I'm looking into tankless, but I am considering other options.

Where it's located, is on an exterior wall, but the builders ran the vent pipe (black, needs changing) to the other exterior wall 12' away, to vent at the same place as the furnace. From my estimation, I can have a new unit vented much closer -- direct vent -- and have no problems.

Question #1: What is the 'typical' lifespan of a direct vent tank, and what is the typical lifespan of a power vent tank (motor seems to be the problem here)? Most online reading indicates a tankless is good for 20 years or so.

The option to go direct vent (or tankless) would mean a new hole in the exterior wall, and plugging/capping the current power vent exhaust. No biggie.

However, I'm looking at this from a cost and ROI perspective too (it's the analyst in me). Tankless should be about $2000-$2500 installed (friend is a gas fitter). Direct vent 50-gal tank will be about $1400 installed. Power vent 50-gal tank will be about $1300 installed. (EDIT: Home Depot 6yr warranty tank installed - Power Vent $1300)
Since the PV and DV tank models typically have shorter lifespans than a tankless, let's say 10 years on average, the cost is a wash after 20 years (as tankless 'should' still be operational then, and tank heaters will have been replaced once, on average, costing more than the original tankless did).

Space savings from tankless are welcomed as there's no other way to easily add 16 square feet of potential-workshop space to my house.

Question #2: What would you do? Tankless (incl. new 7" hole in wall)? Replace the power-vent with a direct vent with new hole in exterior wall? Replace power vent with another power vent and hope the ventor motor doesn't crap out early?

Assuming $300/yr savings vs. renting, the tankless will be "paid off" in about 7 years. The DV will be paid off in about 4 2/3 years, and the PV will be paid off in 4 1/3 years. That's assuming nothing goes wrong before then with each unit.

Tankless has 12 year warranty (Rinnai R75LSi). DV and PV have 6 year warranties (Home Depot or other typical brand tanks).

Curls,
I own a Bosch 1600h tankless water heater. It does require significantly more gas flow than your normal tank water heater, therefor larger pipe, double wall flue... The unit itself is quite compact though, and that can be a big benefit.

My biggest complaint is the "warm up time". You'll run a significant amount of cold water through the heat exchanger before the fire kicks, and even then, you'll continue to wait while it heats up before you'll see hot water at the faucet. Additionally, unlike a tank wh, the water in the lines won't be kept warm by the hot tank that they're connected to. So, the water comes out quite cold for quite a while before it gets warm, then eventually hot.
Even if you turn off the hot water, then back on, you'll get hot, followed by cold, by warm and then eventually hot again.

The cold outside temps definitely has a significant impact on the performance. Takes longer to heat, and not as hot once heated.

I do love the energy savings, particularly because for the last 1 1/2 years, I spent the majority of my time away from my house and used very little hot water. And I do love that I can run back to back hot showers without worrying about ever running out of hot water.